Optimizing stereo-camera position on agricultural robots for cotton height estimation

Abstract

Plant height is an important phenotypic trait used to estimate crop height, biomass, and yield for various crops, including cotton. Traditionally, plant heights were manually measured using rulers and tapes, a tedious and time-consuming task. To address such limitations, several studies have developed and applied different techniques for estimating plant height, including stereo-vision camera systems. However, the lack of standardized camera mounting positions across different studies raises concerns about consistency in plant height measurement as the plant height increases, but the camera position does not. To address these limitations, this study investigates how the mounting position of a stereo-vision camera, specifically the ZED2 stereo-camera from StereoLabs, influences the accuracy of cotton plant height estimation. Furthermore, the study proposes an optimal mounting position for the ZED2 camera for accurate cotton height measurements. In our experiment, we used ten potted cotton plants grown and measured weekly for over six weeks. We mounted the ZED2 camera at five predefined positions (H1, H2, H3, H4, H5) directly above the plant. We ensured that the camera was positioned perpendicular to the plant canopy when measuring and recording the plant heights. The manual measurements served as the ground truth for comparative analysis with camera measurements, using both a mixed-effects model and a simple regression model. Experimental results indicated that there were no statistically significant differences between camera measurements and manual measurements when the camera was 38 to 47 inches above the plant canopy. This observation was also demonstrated by a strong linear correlation between the manual and the camera measurement when we ran a simple linear regression model (R 2 = 0.987). The findings from this study emphasize the importance of mounting cameras at the proposed positions to obtain an accurate estimate of plant height, thereby enhancing agronomic field decisions.

Plant phenotyping relevance

ステレオカメラによる綿花の草丈という植物形質の推定について、カメラ取付位置を最適化し、手測定を基準に精度を検証しているため、フェノタイピング手法が中心である。

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